1. Field of Invention
This invention generally relates to detecting and maintaining good image registration in color image processing.
2. Description of Related Art
Electrophotography, a method of copying or printing documents, is performed by exposing an image representation of a desired original image onto a substantially uniformly charged photoreceptor, such as a belt. In response to that image representation, the photoreceptor discharges to create a latent image of the desired original image on the photoreceptor""s surface. Developing material, or toner, is then deposited onto the latent image to form a developed image. The developed image is then transferred to a final substrate, such as paper. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
Color images may be produced by repeating the above process once for each differently colored toner that is used to make a composite color image. For example, in one color imaging process, referred to herein as the Recharge, Expose and Develop, Image On Image (REaD IOI) process, a charged photoreceptor surface is exposed to an image which represents a first color. The resulting electrostatic latent image is then developed with a first colored toner to form a first color separation image. The charge, expose and develop process is repeated, for example, for a second colored toner, then for a third colored toner, and finally for a fourth colored toner to form second, third and fourth color separation images. The various differently-colored color separation images are placed in superimposed registration with the first developed color separation image so that a desired composite color image results. The composite color image is then transferred and fused onto an image recording substrate or medium.
Registration offsets in a developed image are undesirable because, if the developed image is transferred to a final substrate without adjusting for the registration offsets, the final transferred image will include the registration offsets. That is, each different color separation image will be slightly misregistered, or offset, relative to the other color separation images and/or the receiving substrate. By using registration sensors to register the color separation under a variety of machine conditions without accounting for differences between sensor types, an incorrect number of signals may be detected which may not correctly adjust for the misregistration or offset.
This invention provides color imaging methods and systems where each color separation image is to be registered in a composite manner under a variety of machine conditions.
This invention separately provides systems that calibrate the registration sensors automatically based on set-up data and, using the calibrated sensors, controls the output of the image data for one or more of the color separation images to reduce or eliminate image registration offsets.
This invention further provides methods for calibrating registration sensors by directly measuring set-up marks during a set-up procedure to account for phenomenon caused by variation in machine conditions, such as toner concentration, sensor susceptibility, and toner contamination on the sensor.
The systems and methods of this invention separately provide registration sensors which provide feedback signals for each of at least four colors and for a bare photoreceptor belt, where each registration sensor outputs the feedback signals to a controller during a set-up procedure.
The systems and methods of this invention separately provide a controller that determines the differences between the set-up sensor feedback value for each sensor for each of the four colors and the set-up feedback value for each sensor for the bare photoreceptor belt. The systems and methods of this invention use the determined differences to determine desired operating conditions for each sensor, including an amount of driving current to be applied to the sensor.
In accordance with the systems and methods of this invention, problems in registration, such as misalignment, are reduced or eliminated without being influenced by variations in machine conditions.
In another aspect of the systems and methods of the invention, image data is adjusted based on determined image registration offsets irrespective of variation in machine conditions. In yet another aspect of the systems and methods of this invention, the image processing device outputs an image based on image control data adjusted based on determined image registration offsets.
These and other features and advantages of the systems and methods of this invention are described in or are apparent from the following detailed description of the preferred embodiments.